io: Always use unbuffered input

Before, we often used unbuffered input via the lzma or gzip handlers,
more or less inadvertently.

Change the default file handlers from buffered (stdc FILE) to unbuffered
(POSIX fds).

include/libxml/xmlIO.h

@@ -347,19 +347,24 @@ XMLPUBFUN xmlParserInputPtr
 XMLPUBFUN xmlChar *
 	xmlNormalizeWindowsPath		(const xmlChar *path);
 
+XML_DEPRECATED
 XMLPUBFUN int
 	xmlCheckFilename		(const char *path);
 /**
  * Default 'file://' protocol callbacks
  */
+XML_DEPRECATED
 XMLPUBFUN int
 	xmlFileMatch			(const char *filename);
+XML_DEPRECATED
 XMLPUBFUN void *
 	xmlFileOpen			(const char *filename);
+XML_DEPRECATED
 XMLPUBFUN int
 	xmlFileRead			(void * context,
 					 char * buffer,
 					 int len);
+XML_DEPRECATED
 XMLPUBFUN int
 	xmlFileClose			(void * context);